there are a few things that I used to do regularly with the "Ubuntu Classic" interface and I can't figure out how to do them with the Unity interface (provided it is possible to do them at all):

open a file at a specific location: I used to type Alt+F2 then type the complete path to the file (with tab completion) and then hitting Enter would just open the file. It seems to me that there is no way to do the same thing in Unity. Searching for the filename is not really an option as there may be multiple files with the same name in different locations.

single click window selection: thanks to the windows list applet in the panel, I could switch from one window to the other (within a workspace) with a single click. Can I do this in Unity? it seems to me that this is not possible.

single click workspace switch: thanks to the workspace applet in the panel I could switch to a different workspace with a single click or move a window to another workspace very easily by dragging it in the workspace applet. In Unity I have to move the cursor on the left border, wait that the lancher pops up, click on the workspace switcher, wait that the workspaces pop up and the I have to double-click on the ws I want. This is waaaay to slow. Any other option?

If you install compizconfig-settings-manager you can fiddle with the settings to get certain things to work. For example, I like being able to switch workspaces using the mouse's scroll wheel (with the cursor over the desktop); this can be enabled in the Viewport Switcher module. On my netbook (no mouse) I prefer to stick to keyboard shortcuts; these work quite well in Unity.

As for opening files, that seems like a bug - I've just noticed that if you hit Alt+F2 and start entering the path to a file, it appears to be working (once you've typed /home/ it shows all the folders in /home/; once you get to /home/user/ it shows the files and subdirectories in your home folder, etc, but if you enter a full path and hit enter - or even click on a file once it shows up below the search box - nothing happens). My guess is that the intended behaviour is what you're used to, but it's not working right. I'll take a look on Launchpad, and if there isn't already a bug filed on this, I'll add one.

**Update: After doing a search on Launchpad and asking the developers on one of the bug reports, they suggested the following answer for (1): Use the Files/Folders Lens, but it's not quite there yet.
If you're keyboard-oriented, you can just replace Alt+F2 with Super+F. (Simply tapping the Super key gets you a search ball also, but that will search both files and applications.) Unfortunately, at the moment it only finds 'recent files' but they're hard at work getting full functionality in place for 11.10.

Update: you can get this to work by tapping the Super (windows) key rather than Alt+F2. (And you should only need the file name, not the full path.) There's only one catch - it only works for 'recent' files due to the way Zeitgeist handles things. (See bugs.launchpad.net/unity/+bug/646724) This is a problem if you've done a clean install and keep your docs on a separate partition (or import from a backup).
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Sean FitzpatrickMay 30 '11 at 20:18